Liquid crystal display and method of manufacturing the same

ABSTRACT

The invention relates to a liquid crystal display utilizing a vertically aligned state of liquid crystal molecules when no voltage is applied and to a method of manufacturing the same. 
     The liquid crystal display includes a monofunctional monomer having a structure expressed by X—R (where X represents an acrylate group or a methacrylate group, and R represents an organic group having a steroid skeleton). A liquid crystal material is sandwiched between substrates which is then irradiated with ultraviolet rays to cure the monofunctional monomer, thereby forming a polymer film at an interface of a substrate. The monofunctional monomer has a hydrophobic skeleton such as an alkyl chain and a photoreactive group on one side of the skeleton.

This is a divisional of application Ser. No. 13/449,929, filed Apr. 18,2012, which is a divisional of application Ser. No. 12/779,561, filedMay 13, 2010, now U.S. Pat. No. 8,178,171, issued May 15, 2012, which isa divisional of application Ser. No. 10/809,126, filed Mar. 25, 2004,now U.S. Pat. No. 7,749,575, issued Jul. 6, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display and a methodof manufacturing the same and, more particularly, to a liquid crystaldisplay utilizing a condition in which liquid crystal molecules arevertically aligned when no voltage is applied and a method ofmanufacturing the same.

2. Description of the Related Art

Active matrix type liquid crystal displays (LCDs) that have been widelyused include TN mode liquid crystal displays in which a liquid crystalmaterial having positive dielectric constant anisotropy is aligned suchthat it is in parallel with surfaces of substrates and such that it istwisted at 90 deg. between the substrates which are opposed to eachother. However, the TN mode has a problem in that it provides lowviewing angle characteristics, and various studies are in progress inorder to improve viewing angle characteristics.

As an alternative to this method, MVA (Multi-domain Vertical Alignment)method has been developed in which a liquid crystal material havingnegative dielectric constant anisotropy is vertically aligned and inwhich tilting directions of liquid crystal molecules are regulated byprotrusions and slits provided on surfaces of substrates when a voltageis applied, and the method has successfully improved viewing anglecharacteristics.

An MVA type liquid crystal display will be described with reference toFIGS. 1A, 1B and 2. FIGS. 1A and 1B are perspective views showing theconcept of the MVA type liquid crystal display. FIG. 2 is a conceptualdiagram showing aligning directions of liquid crystal molecules on apixel 7 of the MVA type liquid crystal display as viewed in a directionnormal to a surface of a substrate thereof.

In the MVA type liquid crystal display, as shown in FIGS. 1A and 1B, aliquid crystal material (liquid crystal molecules) 5 having negativedielectric constant anisotropy is vertically aligned between two glasssubstrates 21 and 22. A pixel electrode connected to a ITT which is notshown is formed on the glass substrate 21, and an opposite electrode isformed on the other glass substrate 22. Protrusions 61 and 62 arealternately formed on the pixel electrode and the opposite electrode,respectively. Vertical alignment films which are not shown are formed onthe pixel electrode and the opposite electrode which are not shown andon the protrusions 61 and 62.

When no voltage is applied to the liquid crystal molecules 5 with theTFT in an off-state, as shown in FIG. 1A, the liquid crystal molecules 5are aligned in a direction perpendicular to substrate interfaces. Whenthe TFT is turned on, an electric field acts on the liquid crystalmolecules 5, and tilting directions of the liquid crystal molecules 5are regulated by the structure in which the protrusions 61 and 62 areformed. As a result, the liquid crystal molecules 5 are aligned in aplurality of directions in one pixel as shown in FIG. 1B. For example,when the protrusions 61 and 62 are formed as shown in FIG. 2, the liquidcrystal molecules 5 are aligned in each of directions A, B, C and D.Since the liquid crystal molecules 5 are aligned in a plurality ofdirections when the TFTs are turned on in the MVA type liquid crystaldisplay, preferable viewing angle characteristics can be achieved.

In the above-described MVA method, vertical alignment films do notregulate the tilting directions of the liquid crystal molecules 5.Therefore, there is no need for an alignment processing step such asrubbing that is essential for horizontal aligning methods represented bythe TN method. This is advantageous from the viewpoint of processing inthat the problem of static electricity and waste which occurs during arubbing process is eliminated and in that no washing process is requiredafter an aligning process. Further, since problems such as displayirregularities attributable to variation of a pre-tilt will not occur,there is another advantage in that a cost reduction can be achievedthrough simplification of processes and improvement of yield.

-   Patent Document 1: JP-A-11-95221-   Patent Document 2: JP-A-5-232465-   Patent Document 3: JP-A-8-338993-   Patent Document 4: JP-A-8-036186

Although the MVA method has various advantages as thus described, thesimplification of processes, the improvement of yield and the costreduction can be further encouraged if the existing step for formingvertical alignment films can be omitted. Further, although there is aneed for forming vertical alignment films on mother glasses which areincreasing in size as a result of the recent trend toward greater LCDs,a problem has arisen in that the existing alignment film printingapparatus may become unable to satisfy such a need.

In the existing methods for forming vertical alignment films, there is aphenomenon in which horizontally aligned domains called white lines canremain in a vertically aligned region. There is a need for reducing oreliminating such white lines to suppress reduction in contrast.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a liquid crystal display anda method of manufacturing the same in which the existing step forforming vertical alignment films can be omitted to achieve a costreduction.

It is another object of the invention to provide a liquid crystaldisplay and a method of manufacturing the same in which verticalalignment films can be easily formed even if the mother glasses arelarge-sized.

It is still another object of the invention to provide a liquid crystaldisplay and a method of manufacturing the same in which white lines canbe reduced to suppress reduction in contrast.

The above-described objects are achieved by a liquid crystal displayhaving a liquid crystal material sandwiched between substrates,characterized in that:

the liquid crystal material includes a monomer material having astructure expressed by X—R (where X represents an acrylate group or amethacrylate group and R represents an organic group having a steroidskeleton); and

an ultraviolet-cured substance comprising a system including the monomermaterial is formed at an interface of the substrates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are perspective views showing a schematic configurationof an MVA type liquid crystal display;

FIG. 2 is a plan view showing the schematic configuration of the MVAtype liquid crystal display;

FIGS. 3A and 3B show a basic principle 1 of a liquid crystal display anda method of manufacturing the same in a first mode for carrying out theinvention;

FIGS. 4A and 4B show a basic principle 2 of a liquid crystal display anda method of manufacturing the same in the first mode for carrying outthe invention;

FIGS. 5A to 5D show examples of monofunctional monomer materials havinga steroid skeleton to be mixed in a liquid crystal material of a liquidcrystal display in the first mode for carrying out the invention;

FIGS. 6A to 6D show examples of bifunctional monomer materials having aring structure to be mixed in a liquid crystal material of a liquidcrystal display in the first mode for carrying out the invention;

FIG. 7 shows changes in the voltage holding ratio and the state ofalignment depending on the mixing ratio of a monomer material mixed in aliquid crystal material of a liquid crystal display in the first modefor carrying out the invention;

FIGS. 8A to 8D show examples of divalent organic groups having a steroidskeleton mixed in a liquid crystal material of a liquid crystal displayin the first mode for carrying out the invention;

FIG. 9 shows changes in the voltage holding ratio and the state ofalignment depending on the mixing ratio of a monomer material mixed in aliquid crystal material of a liquid crystal display in the first modefor carrying out the invention;

FIGS. 10A to 10D show examples of monofunctional monomer materials mixedin a liquid crystal material of a liquid crystal display in a secondmode for carrying out the invention;

FIGS. 11A to 11D show examples of monomer materials having a ringstructure mixed in a liquid crystal material of a liquid crystal displayin the second mode for carrying out the invention;

FIGS. 12A and 12B show a phenomenon in which horizontally aligneddomains appearing as white lines are generated in a vertically alignedregion;

FIGS. 13A to 13C show examples of monofunctional monomer materials mixedin a liquid crystal material of a liquid crystal display in the secondmode for carrying out the invention;

FIG. 14 shows changes in the voltage holding ratio and the state ofalignment depending on the mixing ratio of a monomer material mixed in aliquid crystal material of a liquid crystal display in the second modefor carrying out the invention;

FIGS. 15A and 15B show a reduction of horizontally aligned domainsvisually perceived as white line in a vertically aligned region which isachieved by a method of manufacturing a liquid crystal display in athird mode for carrying out the invention;

FIG. 16 shows a relationship between doses of irradiation and voltageholding ratio in the method of manufacturing a liquid crystal display inthe third mode for carrying out the invention;

FIGS. 17A to 17F briefly show LCD manufacturing processes according tothe related art;

FIGS. 18A to 18C, 18B-1, 18B-2, and 18B-3 schematically show a method offorming an alignment control layer after injecting a liquid crystal;

FIG. 19 shows display irregularities which are observed when a liquidcrystal display panel of a 15-inch type active matrix LCD is turned on;

FIG. 20 is a graph showing a comparison between voltage-transmittance(gradation transmittance) characteristics of normal and abnormal partsat liquid crystal injection holes in the case of storage driving;

FIGS. 21A and 21B show the problem of display irregularities at liquidcrystal injection holes using large panels (equivalent to a 15-inchtype) for evaluation of voltage holding ratio which are formed bycombining a pair of substrates having transparent electrodes;

FIG. 22 shows a relationship between a UV irradiation step for a liquidcrystal cell in a fourth mode for carrying out the invention and voltageholding ratio;

FIG. 23 is a graph for explaining how the specific resistance of aliquid crystal material is reduced by additives that are substancesconstituting alignment assisting materials mixed in the liquid crystal;

FIG. 24 shows a result of an examination of changes in voltage holdingratio relative to doses of irradiation light in the vicinity of a liquidcrystal injection hole of a liquid crystal cell in the fourth mode forcarrying out the invention, the examination being performed with theamount of a bifunctional monomer varied;

FIG. 25 shows a result of an examination of changes in voltage holdingratio relative to doses of irradiation light at a central part of theliquid crystal cell in the fourth mode for carrying out the invention,the examination being performed with the amount of the bifunctionalmonomer varied;

FIG. 26 is a graph showing a comparison between voltage holding ratio atthe liquid crystal injection hole of the liquid crystal cell in thefourth mode for carrying out the invention, the holding ratio beingachieved by increasing the amount of the bifunctional monomer B shown inFIG. 23 and increasing the purity of the monofunctional monomer D,respectively;

FIG. 27 is a graph showing a comparison between voltage holding ratio atthe central part of the liquid crystal cell in the fourth mode forcarrying out the invention, the holding ratio being achieved byincreasing the amount of the bifunctional monomer B shown in FIG. 23 andincreasing the purity of the monofunctional monomer D, respectively;

FIG. 28 shows differences between voltage holding ratio at the liquidcrystal injection hole of the liquid crystal cell in the fourth mode forcarrying out the invention depending on the presence and absence of thepolymerization initiator, the amount of the bifunctional monomer B beingincreased from that in FIG. 23;

FIG. 29 shows a result of an examination of changes in voltage holdingratio relative to doses of irradiation light at the central part of theliquid crystal cell in the fourth mode for carrying out the inventiondepending on the presence and absence of the polymerization initiator,the amount of the bifunctional monomer B being increased from that inFIG. 23;

FIG. 30 shows a result of an examination on a relationship between thepurity of a monofunctional monomer and voltage holding ratio at theinjection hole of the liquid crystal cell in the fourth mode forcarrying out the invention;

FIG. 31 shows a result of an examination on a relationship betweenirradiation energy and voltage holding ratio of the liquid crystal cellin the fourth mode of carrying out the invention depending ondifferences in purity between monofunctional monomers D, the examinationhaving been conducted under the same conditions in FIG. 30 except thatthe amount of the bifunctional monomers B was increased by a factor of2.4;

FIG. 32 is a graph of the liquid crystal cell in the fourth mode forcarrying out the invention in which the purity (GC %) of monofunctionalmonomers D are plotted along the abscissa axis and voltage holding ratio(%) are plotted along the ordinate axis;

FIG. 33 shows a section of a liquid crystal panel suitable for use inthe fourth mode for carrying out the invention;

FIG. 34 shows a section of a liquid crystal panel suitable for use inthe fourth mode for carrying out the invention;

FIGS. 35A to 35C show steps of manufacturing a liquid crystal displaypanel by employing a dispenser injection method suitable for use in thefourth mode for carrying out the invention; and

FIGS. 36A to 36C illustrate manufacture of a liquid crystal panel bydispensing two or more kinds of mixed liquid crystals instead of onekind of mixed liquid crystal by employing a dispenser injection methodsuitable for use in the fourth mode for carrying out the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Mode forCarrying Out the Invention

A liquid crystal display and a method of manufacturing the same in afirst mode for carrying out the invention will now be described withreference to FIGS. 3A to 9. In the present mode for carrying out theinvention, two substrates having no vertical alignment film formedthereon are provided opposite to each other to sandwich a liquid crystalmaterial between them. The liquid crystal material includes a monomermaterial having a molecular structure in which director directions ofliquid crystal molecules can be regulated and having a photoreactivegroup on one side of its skeleton. After the liquid crystal material issandwiched between the substrates, an ultraviolet-cured substance(polymer) obtained by curing the monomer material through irradiationwith ultraviolet rays is formed on interfaces of the substrates. Acommon molecular structure in which director directions of liquidcrystal molecules can be regulated is an alkyl chain. A photoreactivegroup is a skeleton which has an unsaturated double bond such as anacrylate group, a methacrylate group, a vinyl group or an allyl groupand which can be polymerized with another molecule when irradiated withultraviolet rays.

FIGS. 3A and 3B show a basic principle 1 of the present mode forcarrying out the invention. Immediately after the liquid crystal isinjected, as shown in FIG. 3A, liquid crystal molecules 5 which aremixed with a monofunctional monomer 2 having a hydrophobic skeleton 2 asuch as an alkyl chain and a photoreactive group 2 b on one side of theskeleton are horizontally aligned. Nothing is formed on the surface of asubstrate 22. When irradiated with ultraviolet rays, as shown in FIG.3B, a polymer film 4 is formed on the surface of the substrate 22 suchthat groups which regulate director directions of the liquid crystalmolecules 5 align the liquid crystal molecules 5 perpendicularly to aninterface. Unlike existing liquid crystals referred to aspolymer-dispersed liquid crystals (PDLCs), alignment is controlled usinga polymer (resin) film 4 in the form of a thin film which is formed onthe surface of the substrate 22 like an alignment film instead offorming a polymer throughout the liquid crystal layer. When polymers areconstituted by only monofunctional monomers 2, the polymers are in astructure in which they are serially arranged as shown in FIG. 3B, andthe polymer film 4 becomes a resin film in which the polymers arephysically deposited on and caught in each other.

FIGS. 4A and 4B show a basic principle 2 of the present mode forcarrying out the invention. When bifunctional monomers 3 each having ahydrophobic skeleton 3 a such as an alkyl chain and photoreactive groups3 b on both sides of the skeleton as shown in FIG. 4A or multifunctionalmonomers having a greater number of photoreactive groups (functionalgroups) are used in addition to monofunctional monomers 2, a polymerfilm 4 in the form of network that is chemically steric is formed, asshown in FIG. 4B. Amore rigid and reliable polymer film 4 can beobtained in this case.

When monofunctional alkyl monomers in which only one photoreactive groupis added to an ordinary alkyl chain C_(n)H₂₊₁ are used to erect liquidcrystal molecules vertically, the vertically aligning property is not sohigh, and a problem remains in that it is difficult to reduce the mixingratio of bifunctional monomers. Substantially no difference is observedin alignment even when alkyl chains are varied from C₁₂ (lauryl) throughC₁₈ (stearyl). This is considered attributable to the fact that a simplealkyl chain as described above has high flexibility and thatcontribution to vertically aligning property becomes smaller as thealkyl chain becomes longer.

Close studies and trials have revealed that the use of a material havinga steroid skeleton as a component of the ultraviolet-cured resin to beformed makes it possible to improve vertical alignment ability. Inparticular, organic groups as shown in FIGS. 5A to 5D are preferableamong groups having a steroid skeleton. By using such a material havinga steroid skeleton, vertically aligning properties higher than thatachievable with simple alkyl monomers can be achieved even when the doseof the material is substantially halved in terms of molar ratio.

In order to maintain the reliability of the liquid crystal display, itis essential to prevent the release of impurity ions into the liquidcrystal. For this purpose, the ultraviolet-cured resin is formed using asystem which has at least one ring structure and which is mixed with abifunctional material having an acrylate group or a methacrylate groupon one end thereof or a material having more functions. Close studiesand trials have revealed that the use of such a material makes itpossible to forma resin film having less monomer residues without addinga polymerization initiator. In particular, it is preferable to usematerials as shown in FIGS. 6A to 6D in which no spacer intervenesbetween a ring structure and an acrylate group or methacrylate group. Incase that a spacer (s) intervenes, it is preferable that there is onlyone spacer —CH₂—.

The ratio of unreacted residues of a multifunctional monomer having twoor more functions as described above decreases as the mixing ratio ofthe monomer is increased, and electrical characteristics such as avoltage holding ratio are improved accordingly. However, it becomesunable to achieve vertical alignment when the ratio is increased beyonda certain level. In order to solve this problem, bifunctional monomershaving a steroid skeleton as shown in FIGS. 5A to 5D are used. Bysubstituting bifunctional monomers having a steroid skeleton asdescribed above for all or part of the bifunctional monomers, it becomespossible to provide a resin film whose electrical characteristics andvertically aligning properties are balanced at a high level and toprovide an excellent liquid crystal display.

A detailed description will follow with reference to specificembodiments and comparative examples.

Embodiment 1-1

Monomers were fabricated which had a steroid skeleton as shown in FIGS.5A to 5D and in which an acrylate group was substituted for an OH groupin the figure. The monomers in an amount of 1.3×10⁻⁴ mol/g weredissolved in a negative liquid crystal A. Bifunctional monomers having aring structure as shown in FIGS. 6A to 6D in an amount of 1.3×10⁵ mol/gthat is one-tenth of the above amount were then dissolved in the liquidcrystal material. The resultant mixed liquid crystals were injected andsealed in evaluation cells. Two glass substrates having ITO (indium tinoxide) films formed thereon as electrodes were used as an evaluationcell, and the substrates were combined with a cell thickness of 4.25 μm.The substrates used were formed with no alignment film and wereirradiated with ultraviolet rays of 1500 mJ/cm² on surfaces thereof.

An observation of the state of alignment of the evaluation cellsimmediately after fabrication revealed that there was fluid alignmentand that both of horizontal alignment and vertical alignment existed.Thereafter, the evaluation cells were annealed for 30 minutes at 90° C.and were irradiated with unpolarized ultraviolet rays of 9000 mJ/cm²after being cooled. An observation of alignment revealed that perfectvertical alignment was achieved throughout the evaluation cells.

Comparative Example 1-1

An experiment similar to Embodiment 1-1 was conducted using a monomermaterial having no steroid skeleton, i.e. lauryl acrylateCH₂═CHCOOC₁₂H₂₅.

As a result, substantially no change in alignment was observed betweenstates before and after irradiation with ultraviolet rays, andpreferable vertical alignment could not be achieved. When the dose ofthe material was gradually increased, vertical alignment was achieved ata dose of 2.4 to 2.5×10⁻⁴ mol/g which was about twice that in theembodiment (the bifunctional monomers were dissolved in the fixed ratioof one-tenth, i.e., in an amount of 2.4×10⁻⁵ mol/g). However, manydefects in the form of white lines were observed in any parts in aninitial state of vertical alignment. A similar experiment conductedusing stearyl acrylate CH₂═CHCOOC₁₈H₃₇ indicated no clear differencefrom lauryl acrylate.

Comparative Example 1-2

An experiment similar to Comparative Example 1-1 was conducted by usinga monomer HDDA having no ring structure instead of bifunctional monomershaving a ring structure as shown in FIGS. 6A to 6D, dissolving it in thesame amount 1.3×10⁻⁵ mol/g in the liquid crystal material, andfabricating an evaluation cell from the resultant mixed liquid crystal.

As a result, substantially no change in alignment was observed betweenstates before and after irradiation with ultraviolet rays similarly tothe Comparative Example 1-1, and vertical alignment was not achievedwhen irradiation was continued with ultraviolet rays of 9000 mJ/cm²unlike Embodiment 1-1. Then, Irg651 of 0.2% by weight as apolymerization initiator was added to the liquid crystal which was thenirradiated with ultraviolet rays, and the liquid crystal as a wholecould be vertically aligned. However, measurement of the voltage holdingratio revealed that there was a significant reduction in the voltageholding ratio around the injection hole.

Comparative Example 1-3

An experiment similar to Comparative Example 1-1 was conducted by usingbifunctional monomers having one or more ring structures as shown inFIGS. 6A to 6D and providing CH₂ between a ring structure and anacrylate group or a methacrylate group (the relationship of FIG. 6D toFIG. 6C), and differences in reactivity were observed. CH₂ was providedin different quantities, i.e., 1, 2, 4 and 6 with the mixing ratio andthe quantity of the monomers added in terms of mol kept unchanged.

As a result, changes before and after irradiation with ultraviolet raysabruptly diminished when two CH₂ were provided substantially regardlessof the number of ring structures and the structure for connecting rings,and vertical alignment was not achieved in samples having four and sixCH₂ after irradiation with ultraviolet rays however great the dose was.

Embodiment 1-2

Lauryl acrylate of 2.4×10⁻⁴ mol/g and bifunctional monomers having ringstructures as shown in FIGS. 6A to 6D were dissolved in a negativeliquid crystal A, and resultant mixed liquid crystals were injected andsealed in evaluation cells. The evaluation cells were fabricated withthe molar ratio of the bifunctional monomers to lauryl acrylate varied.Other conditions for fabrication followed those for Embodiment 1-1, andtwo glass substrates having ITO films formed thereon as electrodes wereused for an evaluation cell and were combined with a cell thickness of4.25 μm. The substrates used had no alignment film formed thereon andwere irradiated with ultraviolet rays of 1500 mJ/cm² on surfacesthereof.

FIG. 7 shows results of evaluation of voltage holding ratio andvertically aligning properties after irradiation with ultraviolet raysof 9000 mJ/cm², the holding period being 1.67 s. The abscissa axis ofFIG. 7 represents mixing ratios between lauryl acrylate and thebifunctional monomers, and the ordinate axis represents relative holdingratio. A holding ratio of 100(%) is the value of a holding ratio in asaturated state. Referring to the symbols above the horizontal arrows inthe figure, the circle represents a region of mixing ratios in whichvertical alignment could be achieved; the triangle represents a regionof mixing ratios in which horizontal alignment partially remained; andthe cross represents a region of mixing ratios in which horizontalalignment remained as it was. As shown in FIG. 7, the voltage holdingratio gradually increased with the ratio of the bifunctional monomers,and saturation was substantially reached at a ratio in the range fromabout 7:1 to 6:1 for any of the materials. However, vertically aligningproperties gradually deteriorated on the contrary, and some regionsappeared with insufficient verticalness around when the mixing ratiodropped below 10:1. The results were conflicting in that verticalalignment cannot be achieved under conditions that allow the bestholding ratio to be achieved.

A similar experiment was conducted with the half of the dose of thebifunctional monomers replaced with bifunctional monomers havingstructures as shown in FIGS. 8A to 8D which had steroid skeletons and inwhich OH groups were acrylate groups. FIG. 9 shows the result. Theabscissa axis of FIG. 9 represents mixing ratios between lauryl acrylateand the bifunctional monomers, and the ordinate axis represents relativeholding ratio. Referring to the symbols above the horizontal arrows inthe figure, the circle represents a region of mixing ratios in whichvertical alignment could be achieved; the triangle represents a regionof mixing ratios in which horizontal alignment partially remained; andthe cross represents a region of mixing ratios in which horizontalalignment remained as it was. As shown in FIG. 9, while no significantchange was observed in the process of the change in the voltage holdingratio, vertical alignment could be achieved in an increased range toallow both of the voltage holding ratio and vertical alignment to beachieved at a high level which had not been achievable so far.

As described above, since the use of the present mode for carrying outthe invention eliminates the need for an alignment film forming step forliquid crystal displays, in particular, vertical alignment type displaysrepresented by MVA types, a significant cost reduction can be achieved.

Further, a liquid crystal alignment control layer can be easily formedeven on an ultra-large mother glass which cannot be sufficiently handledwith alignment film printing apparatus according to existing methodswithout being affected by the size of the same. The invention also makesit possible to provide liquid crystal displays utilizing substrateswhich are difficult to print such as substrates having greatirregularities and substrates having curved surfaces.

Second Mode for Carrying Out the Invention

A liquid crystal display and a method of manufacturing the same in asecond mode for carrying out the invention will now be described withreference to FIGS. 10A to 14. As described above, not so high verticalalignment is achieved by monofunctional alkyl monomers in which only onephotoreactive group is added to an ordinary alkyl chain C_(n)H_(2n+1) inorder to align the liquid crystal molecules vertical.

Close studies and trials revealed that vertical alignment ability couldbe improved by using a material system in which a ring structure isintroduced between ordinary alkyl chains as a component of theultraviolet-curved resin to be formed. More specifically, the liquidcrystal material includes a monomer material having a structureexpressed by:

(where X represents an acrylate group or methacrylate group; Arepresents a benzene ring or cyclohexane ring; R₁ represents an alkylgroup or alkoxy group having carbon atoms in a quantity in the rangefrom 1 to 20; a represents 0 or 1; m represents an integral number inthe range from 0 to 10; and n represents an integral number in the rangefrom 0 to 2) or a monomer material having a structure expressed by:

(where X represents an acrylate group or methacrylate group; Arepresents a benzene ring or cyclohexane ring; R₁ represents an alkylgroup or alkoxy group having carbon atoms in a quantity the range from 1to 20; R₂ represents CH₃ or a fluorine atom; a represents 0 or 1; mrepresents an integral number in the range from 0 to 10; and nrepresents an integral number in the range from 0 to 2), and the liquidcrystal material is sandwiched between substrates and is then irradiatedwith ultraviolet rays to cure the monomer material, thereby forming anultraviolet-cured substance on an interface of a substrate.

At this time, the value n is preferably 0 from the viewpoint of verticalaligning power, and a preferable result will then be obtained withregard to vertical aligning power relative to the dose in terms of molarratio. However, solubility is slightly reduced. Further, the value a ispreferably 0 to reduce the molecular weight, and the value m is set at 0in this case to make it possible to provide a structure in which areacting group is directly coupled with a benzene ring. Such values maybe appropriately set with respect to the liquid crystal to be mixed toachieve higher effects.

The most significant problem in utilizing the above-described monomer issolubility. A material is useless if it cannot be dissolved in a liquidcrystal that is the base material to be used with the same in an amountrequired to achieve vertical alignment however high vertical aligningpower it may have. Close studies and trials revealed that a resin filmcapable of achieving preferable vertical alignment cannot be formedunless the sum of the number of carbon atoms of the group represented byR₁ and the integral number n is 20 or less. It was also reveled that theadvantage of the monomer over alkyl monomers in the related art isreduced when the sum of the number of carbon atoms of the grouprepresented by R₁ and the integral number n is less than 5. Thus, thesum of the number of carbon atoms of the group represented by R₁ and theintegral number n must be in the range from 5 to 20 as a requirement forforming the monomer material. Especially, the group R₁ is desirably analkyl group having about 6 to 12 carbons or an alkoxyl group that issimilar to the same in length.

CH₃ or a fluorine atom may be introduced as R_(z) in the formula toimprove the vertical aligning power and solubility. FIGS. 10A to 10Dshow examples of monofunctional monomer materials in the present modefor carrying out the invention. The use of such a material makes itpossible to achieve vertically aligning properties higher than thoseachievable with a simple alkyl monomer even when the dose of the formeris about one-half the dose of the latter in terms of molar ratio.

In order to maintain the reliability of a liquid crystal display, it isessential to prevent the release of impurity ions into the liquidcrystal. For this purpose, an ultraviolet-cured resin is formed using asystem which has at least one ring structure and which is mixed with abifunctional material having an acrylate group or a methacrylate groupon one end thereof or a material having more functions. Close studiesand trials have revealed that the use of such a material makes itpossible to form a resin film having less monomer residues withoutadding a polymerization initiator. In particular, it is preferable touse materials as shown in FIGS. 11A to 11D in which no spacer intervenesbetween a ring structure and an acrylate group or methacrylate group. Incase that a spacer (s) intervenes, it is preferable that there is onlyone spacer —CH₂—.

The ratio of unreacted residues of monomers having two or more functionsas described above decreases as the mixing ratio of the monomers isincreased, and electrical characteristics such as a voltage holdingratio are improved accordingly. However, it becomes unable to achievevertical alignment with an alkyl monomer according to the related artwhen the ratio is increased beyond a certain level. However, the use ofa monofunctional monomer as shown in the present mode for carrying outthe invention solves the problem and makes it possible to provide aresin film whose electrical characteristics and vertically aligningproperties are balanced at a high level and to provide an excellentliquid crystal display.

A detailed description will follow with reference to specificembodiments and comparative examples.

Embodiment 2-1

Monomers were fabricated which had structures including a ring structurebetween alkyl chains as shown in FIGS. 10A to 10D. The monomers in anamount of 1.3×10⁻⁴ mol/g were dissolved in a negative liquid crystal A.Bifunctional monomers having a ring structure as shown in FIGS. 11A to11D in an amount of 1.3×10⁻⁵ mol/g that is one-tenth of the above amountwere then dissolved in the liquid crystal A. The resultant mixed liquidcrystals were injected and sealed in evaluation cells. Two glasssubstrates having ITO films formed thereon as electrodes were used as anevaluation cell, and the substrates were combined with a cell thicknessof 4.25 μm. The substrates used were formed with no alignment film andwere irradiated with ultraviolet rays of 1500 mJ/cm² on surfacesthereof.

An observation of the state of alignment of the evaluation cellsimmediately after fabrication revealed that there was fluid alignmentand that both of horizontal alignment and vertical alignment existed.Thereafter, the evaluation cells were annealed for 30 minutes at 90° C.and were irradiated with unpolarized ultraviolet rays of 9000 mJ/cm²after being cooled. An observation of alignment revealed that perfectvertical alignment was achieved throughout the evaluation cells. FIGS.12A and 12B show a phenomenon in which horizontally aligned domainsappearing as white lines are formed in a vertically aligned region.Although defects in the form of white lines were observed in some partsin an initial state of vertical alignment as shown in FIG. 12B, theycompletely disappeared when a pressure was applied to those locationsand did not appear again thereafter.

Comparative Example 2-1

An experiment similar to Embodiment 2-1 was conducted using an ordinaryalkyl monomer material having no ring structure between alkyl chains,i.e. lauryl acrylate CH₂═CHCOOC₁₂H₂₅.

As a result, substantially no change in alignment was observed betweenstates before and after irradiation with ultraviolet rays, andpreferable vertical alignment could not be achieved. When the dose ofthe material was gradually increased, a vertically aligned state wasachieved at a dose of 2.4 to 2.5×10⁻⁴ mol/g which was about twice thatin the embodiment (the bifunctional monomers were dissolved at the fixedratio of one-tenth, i.e., in an amount of 2.4×10⁻⁵ mol/g). However, manydefects in the form of white lines were observed in the verticallyaligned state as shown in FIG. 12A. Thus, contrast was low, androughness was noticeable in display of black and was not so much reducedeven when a pressure was applied to locations with roughness. A similarexperiment conducted using stearyl acrylate CH₂═CHCOOC₁₈H₃₇ indicated noclear difference from lauryl acrylate.

Comparative Example 2-2

An experiment similar to Comparative Example 2-1 was conducted by usinga monomer HDDA having no ring structure instead of bifunctional monomershaving a ring structure as shown in FIGS. 11A to 11D, dissolving it inthe same amount 1.3×10⁻⁵ mol/g in the liquid crystal material, andfabricating an evaluation cell from the resultant mixed liquid crystal.

As a result, no significant change in alignment was observed betweenstates before and after irradiation with ultraviolet rays just as inComparative Example 2-1, and perfect vertical alignment was not achievedwhen irradiation was continued with ultraviolet rays of 9000 mJ/cm²unlike Embodiment 2-1. Then, Irg651 of 0.2% by weight as apolymerization initiator was added to the liquid crystal which was thenirradiated with ultraviolet rays, and the liquid crystal as a wholecould be vertically aligned. However, measurement of the voltage holdingratio revealed that there was a significant reduction in the voltageholding ratio around the injection hole.

Embodiment 2-2

Solubility and vertically aligning properties were evaluated usingmaterials having alkyl skeleton portions with different lengths. FIGS.13A to 13C show examples of the materials used. First, when the materialshown in FIG. 13A was used, the material dissolved in the liquid crystalin an amount of 1.5% by weight but deposited during a process of vacuuminjection when the amount was 1.8% by weight. A cell was fabricatedunder the condition of 1.5% by weight at which the material was soluble,and the state of alignment was observed after irradiating the same withultraviolet rays, which revealed no significant change from the statebefore the irradiation. At this time, the sum of the number of carbonatoms of the group represented by R₁ and the integral number m in theabove formula was 25.

Solubility was then observed with the length of the alkyl skeletonportion gradually reduced. As a result, the material became soluble inan amount of 2.5% or more by weight when the sum of the number of carbonatoms of the group R₁ and the integral number m became about 20. Sincethis means a reduction of about 20% in terms of molecular weight, thesoluble amount in terms of molar weight was increased by a factor of twoor more.

The material was dissolved in an amount of 1.3×10⁻⁴ mol/g in a negativeliquid crystal A. just as in Embodiment 2-1, and bifunctional monomershaving ring structures as shown in FIGS. 11A to 11D were then dissolvedin an amount of 1.3×10⁻⁵ mol/g that is one-tenth of the above amount.Cells were fabricated using resultant mixed liquid crystals. Anobservation of alignment after irradiation with ultraviolet raysrevealed that perfect vertical alignment was achieved throughout theevaluation cells.

When the lengths of the alkyl skeleton portions of the monomers werereduced as shown in FIGS. 13B and 13C, vertical alignment was achievedbut a phenomenon was observed, in which many white lines shown in FIG.12A became visible to reduce the advantage of the materials overordinary alkyl monomers. At that time, the sum of the number of carbonatoms of the group R₁ and the integral number m was about 3 or 4. Whenthe lengths were further reduced, it became impossible to achieveperfect vertical alignment without relying upon other skeleton portions.

Embodiment 2-3

Lauryl acrylate of 2.4×10⁻⁴ mol/g and bifunctional monomers having ringstructures as shown in FIGS. 11A to 11D were dissolved in a negativeliquid crystal A, and resultant mixed liquid crystals were injected andsealed in evaluation cells. The evaluation cells were fabricated withthe molar ratio of the bifunctional monomers to lauryl acrylate varied.Other conditions for fabrication followed those for Embodiment 2-1, andtwo glass substrates having ITO films formed thereon as electrodes wereused for an evaluation cell and were combined with a cell thickness of4.25 μm. The substrates used had no alignment film formed thereon andwere irradiated with ultraviolet rays of 1500 mJ/cm² on surfacesthereof.

Results of evaluation of voltage holding ratio in a holding period of1.67 s and vertically aligning properties after irradiation withultraviolet rays of 9000 mJ/cm² were the same as those in FIG. 7 in thefirst mode for carrying out the invention. A holding ratio of 1.0 is thevalue of a holding ratio in a saturated state. As illustrated, thevoltage holding ratio gradually increased with the ratio of thebifunctional monomers, and saturation was substantially reached at aratio in the range from about 7:1 to 6:1 for any of the materials.However, vertically aligning properties gradually deteriorated on thecontrary, and some regions appeared with insufficient verticalnessaround when the mixing ratio dropped below 10:1. The results wereconflicting in that vertical alignment cannot be achieved underconditions that allow the best holding ratio to be achieved.

A similar experiment was conducted with the monomers replaced withmonomers having structures as shown in FIGS. 10A to 10D which had a ringstructure between alkyl chains. FIG. 14 shows the result. The abscissaaxis of FIG. 14 represents mixing ratios between the monomer materialsin the present mode for carrying out the invention and the bifunctionalmonomers, and the ordinate axis represents relative holding ratio.Referring to the symbols above the horizontal arrows in the figure, thecircle represents a region of mixing ratios in which vertical alignmentcould be achieved; the triangle represents a region of mixing ratios inwhich horizontal alignment partially remained; and the cross representsa region of mixing ratios in which horizontal alignment remained as itwas. As shown in FIG. 14, while no significant change was observed inthe process of the change in the voltage holding ratio, verticalalignment could be achieved in an increased range to allow both of thevoltage holding ratio and vertical alignment to be achieved at a highlevel which had not been achievable so far.

As described above, since the use of the present mode for carrying outthe invention eliminates the need for an alignment film forming step forliquid crystal displays, in particular, vertical alignment type displaysrepresented by MVA types, a significant cost reduction can be achieved.

Further, a liquid crystal alignment control layer can be easily formedeven on an ultra-large mother glass which cannot be sufficiently handledwith alignment film printing apparatus according to existing methodswithout being affected by the size of the same. The invention also makesit possible to provide liquid crystal displays utilizing substrateswhich are difficult to print such as substrates having greatirregularities and substrates having curved surfaces.

Third Mode for Carrying Out the Invention

A liquid crystal display and a method of manufacturing the same in athird mode for carrying out the invention will now be described withreference to FIGS. 15A, 15B and 16. In the present mode for carrying outthe invention, a method will be described which is more effective thanmethods in the related art in reducing or completely suppressing whitelines visually perceived in domains that remain in horizontal alignmentinstead of being vertically aligned (see FIGS. 15A and 15B). It has beendifficult to suppress the generation of white lines at a process offorming a resin film on a liquid crystal panel sandwiching a liquidcrystal layer including a polymeric material by irradiating the panelwith light. The difficulty originates in the fact that when a systemincluding a polymeric material is vertically aligned as a result of areaction with the irradiating light, the tilt of liquid crystalmolecules that stand up from a horizontal position greatly variesbetween adjoining regions to leave some horizontally aligned regions.

Close studies and trials revealed that white lines can be reduced to alevel lower than that achievable with methods in the related art orcompletely suppressed by making tilt differences small between regionsthat are uniformly reacting in the liquid crystal panel, i.e., regionsthat are being vertically aligned during the reaction of the systemincluding the polymeric material to thereby eliminate regions left inhorizontal alignment.

It has revealed that a role for a wavelength in the range from 300 nm to400 nm in the reaction of the system including the polymeric material isvery important. Further, it has revealed that liquid crystal displaypanels having high reliability with white lines reduced or eliminatedcan be manufactured by appropriately controlling the irradiationconditions that are, for example, the amount of dose of irradiation,accumulated intensity or ratio of long and short wavelength.

The use of manufacturing a liquid crystal display in the present modefor carrying out the invention makes it possible to suppress reductionof contrast attributable to white lines and to thereby provide anexcellent liquid crystal display.

A detailed description will now be made with reference to specificembodiments and comparative examples.

Embodiment 3-1

A monofunctional monomer having acrylate groups at alkyl chains having11 to 18 CH₂, a diacrylate type bifunctional monomer having a ringstructure, and an initiator were dissolved in a negative liquid crystalA, and substrates which have no alignment film formed thereon and whichhas been subjected to a UV process on surfaces thereof are combined witha cell thickness of 4.25 μm to fabricate a 15-inch type panel. Anobservation of the state of alignment of the liquid crystal panelimmediately after the fabrication revealed that there was fluidalignment and that both of horizontal alignment and vertical alignmentexisted. Thereafter, the liquid crystal panel was annealed for 30minutes at 90° C. and was irradiated with unpolarized ultraviolet raysof 9000 mJ/cm² after being cooled. An observation of alignment revealedthat vertical alignment had been achieved throughout the liquid crystalpanel.

FIGS. 15A and 15B show states of generation of white lines on the panelthus fabricated depending on light sources. FIG. 15A shows state ofwhite lines generated as a result of irradiation with 1 mJ/cm² ofirradiation amount. FIG. 15B shows state of white lines generated as aresult of irradiation with 9 J/cm² of irradiation amount. As shown inFIGS. 15A and 15B, when irradiated with 9 J/cm² or more of irradiationamount, the liquid crystal display panel could be fabricated with lesswhite lines and display irregularities.

FIG. 16 shows the relationship between doses of irradiation and holdingratio thus identified. The abscissa axis of FIG. 16 represents doses ofirradiation, and the ordinate axis represents voltage holding ratio. Asshown in FIG. 16, doses of irradiation in the range 30000 J/cm² or lessare suitable for irradiating light of wavelength in the range from 300nm to 400 nm from the viewpoint of reliability, and irradiation in dosesgreater than the range results in low reliability.

Embodiment 3-2

In an experiment similar to Embodiment 3-1, reduction of reliability inthe neighborhood of the injection hole could be prevented by using avisible light sealer. Reduction of reliability attributable to breakageof liquid crystal molecules including the polymeric material could beprevented by irradiating them with a wavelength in the range from 200 nmto 330 nm with intensity that was 0 to 20% or less of the intensity ofwavelengths in the range from 200 nm to 800 nm. Further, reduction ofreliability could be prevented by using multi-step irradiation in whicha first cycle of irradiation was performed with light of low intensityand followed by second and later cycles of irradiation with higherintensity.

Embodiment 3-3

In an experiment similar to Embodiment 3-1, scanning irradiation wascarried out. Before scanning irradiation was used, the luminancedistribution of 15-inch type panel had a maximum variation of 30% inirradiation intensity, and the variation was reduced to 10% or less whenscanning irradiation wad used. Scanning irradiation thus suppressed thegeneration of white lines and allowed the liquid crystal panel to befabricated with less display irregularities.

Embodiment 3-4

An experiment similar to Embodiment 3-1 was conducted using substrateswhich had been subjected to plasma processing on surfaces thereof. Thesubstrates allowed a liquid crystal panel having less displayirregularities to be fabricated when compared to substrates which hadnot been subjected to any surface modifying process. Similarly,absorption of monomers onto the surfaces of the substrates was preventedby applying a voltage or heat when the liquid crystal including thepolymeric material was injected to reduce the density distribution ofthe monomers, which allowed a liquid crystal panel to be fabricated withless display irregularities.

Embodiment 3-5

An experiment similar to Embodiment 3-1 was conducted using horizontallyaligning spacers. The generation of white lines was not observed on aliquid crystal panel utilizing the horizontally aligning spacers.Further, the surface tension of the horizontally aligning spacers isdesirably 40 dyn/cm or more. When a press process was performed in anexperiment similar to Embodiment 3-1, white lines could be reduced.

As described above, since the use of the present mode for carrying outthe invention eliminates the need for an alignment film forming step forliquid crystal displays, in particular, vertical alignment type displaysrepresented by MVA types, a significant cost reduction can be achieved.

Further, a liquid crystal alignment control layer can be easily formedeven on an ultra-large mother glass which cannot be sufficiently handledwith alignment film printing apparatus according to existing methodswithout being affected by the size of the same. The invention also makesit possible to provide liquid crystal displays utilizing substrateswhich are difficult to print such as substrates having greatirregularities and substrates having curved surfaces.

Fourth Mode for Carrying Out the Invention

A liquid crystal display and a method of manufacturing the same in afourth mode for carrying out the invention will now be described withreference to FIGS. 17A to 36C. FIGS. 17A to 17F schematically illustrateLCD manufacturing processes according to the related art. According toTN types and MVA types in the related art, an alignment film 30 isformed on a transparent substrate 21 made of glass or plastic as shownin FIG. 17A (FIG. 17B). As occasions demand, a rubbing process isperformed in which the alignment film 30 is rubbed with a roller aroundwhich a cloth is wound as shown in FIG. 17C. Then, another transparentsubstrate 22 which has been subjected to similar processes is providedopposite to the transparent substrate 21 (FIG. 17D), and the substratesare combined with a seal material 31 applied to the peripheries thereof.Next, a liquid crystal 5 is injected through a liquid crystal injectionhole that is an opening in part of the seal material 31 (FIG. 17E). Theliquid crystal injection hole is then closed to complete the liquidcrystal panel (FIG. 17F). A dispenser-injection method may be used forthe injection of the liquid crystal instead of vacuum injection asdescribed above.

While the alignment film 30 is formed before the liquid crystal 5 isinjected in the method shown in FIGS. 17A to 17F, a liquid crystaldisplay panel has been invented in which a layer having an alignmentcontrolling function is formed after the liquid crystal is injected asindicated in the above-described modes for carrying out the invention.FIGS. 18A to 18C schematically show a method for forming an alignmentcontrol layer after a liquid crystal is injected. First, two substrates21 and 22 to which no alignment film 30 has been applied yet arecombined so as to leave a predetermined cell gap between them (FIG.18A). Next, as shown in FIG. 18B, a liquid crystal 5′ which is a mixtureof a liquid crystal material 5 and alignment control materials such asultraviolet-cured monomers or oligomers (hereinafter generally referredto as monomers) is injected to form an alignment control layer 30′ inthe layer including the liquid crystal as shown in FIG. 18C, therebyvertically aligning the liquid crystal molecules 5. The step of formingthe alignment control layer 30′ will be described in more detail usingFIGS. 18B-1 to 18B-3. All of the figures show the neighborhood of thesubstrate 21. As shown in FIG. 18B-1, UV light is directed to a surfaceof the substrate. Thus, as shown in FIG. 18B-2, monomers M at theinterface between the mixed liquid crystal 5′ and the substrate 21 arepolymerized into a polymer P1. As irradiation with UV light is continuedfurther, a polymer P2 aligned vertically to the polymer P1 at theinterface with the substrate is formed as shown in FIG. 18B-3, and thepolymers P1 and P2 function as a vertical alignment control layer toalign the liquid crystal molecules 5 vertically.

The above-proposed technique primarily relates to the alignment of aliquid crystal, and no mention has been made on electricalcharacteristics of a liquid crystal cell. In general, an active matrixLCD having switching elements such as TFTs (thin film transistors) musthave a high voltage holding ratio at the liquid crystal cell thereof inlight of its principle. The proposed technique in the related art has aproblem in that display irregularities occur because a high voltageholding ratio cannot be maintained.

FIG. 19 shows display irregularities 16 which are observed when a liquidcrystal display panel 10 of a 15-inch type active matrix LCD is turnedon. For example, display in halftones may result in displayirregularities 16 which are regions appearing darker than a centralregion of the screen, the irregularities spreading from liquid crystalinjection holes 14 that are openings in a seal material 12. FIG. 20 is agraph showing a comparison between voltage-transmittance (gradationtransmittance) characteristics of normal and abnormal parts in the caseof storage driving. It will be understood that the voltage-transmittancecharacteristics of an abnormal part having a light display irregularity(the line connecting symbols ▪) are shifted toward a high voltage sidefrom those of a normal part (the line connecting symbols ♦) and thecharacteristics of another abnormal part having a dark displayirregularity (the line connecting symbols ▴) are further shifted towardthe high voltage side. This indicates that the voltage holding ratio ofthe liquid crystal is low in positions where display irregularitiesoccur. An irregular part has a lower voltage holding ratio, the darkerthe part is. The present mode for carrying out the invention is aimed atimproving the voltage holding ratio of a liquid crystal while aligningliquid crystal molecules vertically.

FIGS. 21A and 21B show the problem using large panels (equivalent to a15-inch type) for evaluation of voltage holding ratio which are formedby combining a pair of substrates having transparent electrodes insteadof a TFT substrate and a CF substrate. The figures show results ofmeasurement of voltage holding ratio of liquid crystal cells in which asubstrate A having a plurality of linear electrodes a-1 to a-n formed inan X-direction and a substrate B having a plurality of linear electrodesb-1 to b-n formed in a Y-direction are combined in a face-to-facerelationship and in which the linear electrodes a and b are provided soas to form a matrix in combination with each other. FIG. 21A showsvoltage holding ratio (VHR; %) measured on a liquid crystal layer afterirradiating the same with UV having an irradiation energy of 300 mJ/cm²,the layer being made of a liquid crystal material in which apolymerization initiator G to be described later is mixed in a monomermaterial D in an amount of 50% by weight (1% by weight of the liquidcrystal material as a whole). FIG. 21B shows voltage holding ratio (VHR;%) measured on a liquid crystal layer after irradiating the same with UVhaving an irradiation energy of 300 mJ/cm², the layer being made of aliquid crystal material in which the polymerization initiator G to bedescribed later is mixed in the monomer material D in an amount of 2.5%by weight (0.05% by weight of the liquid crystal material as a whole).Both of the figures indicate that the voltage holding ratio is low inthe vicinity of an injection hole (in the vicinity of a position wherethe electrode a-4 in the X-direction and the electrode b-1 in theY-direction intersect with each other).

FIG. 22 shows a relationship between a UV irradiation step for a liquidcrystal cell in the present mode for carrying out the invention andvoltage holding ratio. The abscissa axis of the figure representsirradiation energy (J), and the ordinate axis represents voltage holdingratio (%). The liquid crystal material used is a liquid that is amixture of a liquid crystal A (98% by weight), a monofunctional monomerD (1.825% by weight) (91.7% of which is unrefined), a bifunctionalmonomer B (0.125% by weight) and an initiator G (0.05% by weight). Theintensity of the irradiating UV is 0.5 mW/cm². As shown in FIG. 22,voltage holding ratio change depending on the irradiation energy oflight (which is ultraviolet rays in this case) with which the liquidcrystal cell is irradiated. The line connecting symbols ∘ in the figurerepresents changes in a voltage holding ratio near an injection holedepending on changes in the irradiating energy, and the line connectingsymbols ♦ in the figure represents changes in a voltage holding ratio ina central part of the cell depending on the irradiating energy.

FIG. 22 also shows that the voltage holding ratio are low when themonomers which are alignment assisting materials present in the liquidcrystal cell do not react or react insufficiently. The amount ofresidual monomers can be easily analyzed by disassembling the liquidcrystal cell to collect the liquid crystal from substrate surfaces usingan organic solvent and analyzing it using gas chromatography. Asindicated by the three straight lines at the bottom of FIG. 22, thebifunctional monomer is consumed to leave no residue at a first phase ofreaction and the polymerization initiator is consumed to leave noresidue at a second phase of reaction. When the voltage holding ratio ofthe liquid crystal cell is reduced, the monofunctional monomer is leftin a greater amount among the alignment assisting materials, and what isrequired is to cause a reaction of the monomer which has not reactedyet. Although the reaction of the monomer is promoted by increasing theirradiating energy, the survival rate will not become 0. Sincedeterioration of the liquid crystal material itself is caused byirradiation beside the problem of the reaction of the alignmentassisting material, the irradiation must be performed within a requiredrange.

FIG. 23 is a graph for explaining how the specific resistance of theliquid crystal material is reduced by additives that are substancesconstituting the alignment assisting materials mixed in the liquidcrystal. The abscissa axis represents materials in various conditionssuch as the liquid crystal A, monomers B, C, D and E, and polymerizationinitiators F and G. Specific resistances (Ωcm) are shown along theordinate axis in logarithmic representation. As shown in FIG. 23, theliquid crystal A has a specific resistance of 1.67×10¹⁴ Ωcm when it isnot heated. The specific resistance of the liquid crystal A is decreasedto 4.25×10¹³ Ωcm when subjected to a heating process for 20 minutes at90° C. The specific resistance of the liquid crystal A after theaddition of each material shown in FIG. 23 is a value obtained at a dosethat is 1% of the liquid crystal A and after performing a heatingprocess for 20 minutes at 90° C.

It is apparent from FIG. 23 that there is a small reduction of thespecific resistance when the bifunctional monomers B (M=294, solid,purity: 99.8%) and C (M=366 or more, solid) are added and that there isa great reduction when the monofunctional monomers D (M=240, liquid,purity: 91.8%) and E (M=324, liquid, purity: 99.2%) are added. It iswell known that it is required to inject a liquid crystal materialhaving a high specific resistance in order to achieve a high voltageholding ratio. It is therefore required to eliminate unreactedmonofunctional monomers in a mixed liquid crystal.

The purity of a monomer has a significant influence on the voltageholding ratio. A monomer having a low purity includes a great amount ofimpurities, which can cause a great reduction of the voltage holdingratio. In the present embodiment, the purity of a monomer is representedin terms of GC (%) used in gas chromatography that is normallyperformed.

There is a certain limit on the improvement of the voltage holding ratiowhen it is pursued only by increasing the dose of irradiation. Ananalysis on reaction processes revealed that a bifunctional monomer isfirst consumed to come short relative to a monofunctional monomer underconditions employed in the related art. It was found that it is verymuch effective to increase the amount of a bifunctional monomer and toirradiate it with light sufficiently in order to reduce the survivalrate of a monofunctional monomer.

Thus, it was found that a bifunctional monomer plays a very importantrole in causing efficient reaction (consumption) of a monofunctionalmonomer. FIGS. 24 to 29 show results of an examination on changes in thevoltage holding ratio relative to doses of irradiation conducted byvarying the amounts of bifunctional monomers. In each of the figures,the abscissa axis represents irradiation energy (J/cm²), and theordinate represents voltage holding ratio (%).

FIG. 24 shows an effect that occurs at a liquid crystal injection holeof a liquid crystal cell as a result of an increase in the amount of thebifunctional monomer B shown in FIG. 23. The line connecting symbols ▴in the figure represents a result of an arrangement according to therelated art using a liquid crystal material that is the liquid crystal Ashown in FIG. 23 mixed with the monofunctional monomer D, thebifunctional monomer B in a normal amount, and the polymerizationinitiator G (M=256, solid, purity: 99.8%). The ion density is in therange from 300 to 500 pC/cm². The line connecting symbols ∘ represents aresult of an increase in the amount of the bifunctional monomer B. It isapparent that the voltage holding ratio was significantly improved to96.8%. The ion density is in the range from 50 to 90 pC/cm². FIG. 25 issimilar to FIG. 24 except that it shows results obtained in a centralpart of the liquid crystal cell. The ion density is in the range from120 to 180 pC/cm² in the result represented by the line connectingsymbols ▴ in the figure. The line connecting symbols ∘ represents animprovement of the voltage holding ratio to 98.1%, the ion density beingin the range from 30 to 60 pC/cm². Thus, a preferable voltage holdingratio is obtained by increasing the amount of the bifunctional monomer Balso in the central part of the cell. The difference between voltageholding ratio at the liquid crystal injection hole and the central partcan be reduced by increasing the amount of the bifunctional monomer Bfurther.

FIG. 26 is a graph showing a comparison between voltage holding ratio atthe liquid crystal injection hole of the liquid crystal cell, theholding ratio being achieved by increasing the amount of thebifunctional monomer B shown in FIG. 23 and increasing the purity of themonofunctional monomer D, respectively. The line connecting symbols ♦ inthe figure represents a result of the use of a liquid crystal materialthat is the liquid crystal A shown in FIG. 23 mixed with themonofunctional monomer D with an increased purity of 97.7%, thebifunctional monomer B in a normal amount, and the polymerizationinitiator G. The line connecting symbols ∘ represents a result of theuse of a liquid crystal material that is mixed with the monofunctionalmonomer D with purity of 91.8%, the bifunctional monomer B in anincreased amount, and the polymerization initiator G. It is apparentthat a more significant improvement of the voltage holding ratio isachieved by increasing the amount of the bifunctional monomer thanincreasing the purity of the monofunctional monomer. FIG. 27 is similarto FIG. 26 except that it shows results obtained at the central part ofthe liquid crystal cell. A preferable voltage holding ratio is obtainedby increasing the amount of the bifunctional monomer B also in thecentral part of the cell.

FIG. 28 shows differences between voltage holding ratio that depend onthe presence and absence of the polymerization initiator, the amount ofthe bifunctional monomer B being increased from that in FIG. 23. Theline connecting symbols x in the figure represents a result of the useof a liquid crystal material that is the liquid crystal A shown in FIG.23 mixed with the monofunctional monomer D, the bifunctional monomer Bwith an increased amount, and no polymerization initiator. When nopolymerization initiator is added, liquid crystal molecules arevertically aligned with an irradiation energy of 3 J or more. A voltageholding ratio of 97.5% is achieved at an irradiation energy of 9 J. Theion density is in the range from 22 to 30 pC/cm². The line connecting ∘represents a result of the use of a liquid crystal material that is theliquid crystal A mixed with the monofunctional monomer D, thebifunctional monomer B in an increased amount, and the polymerizationinitiator G. The line is not significantly different from the lineconnecting symbols x in the figure, which indicates that the presence orabsence of the polymerization initiator does not significantlycontribute to voltage holding ratio. The ion density is in the rangefrom 500 to 90 pC/cm² when there is the polymerization initiator. FIG.29 shows a result obtained at the central part of the liquid crystalcell, the result being similar to that shown in FIG. 28. Liquid crystalmolecules are vertically aligned at an irradiation energy of 3 J or morewhen there is no polymerization initiator. A voltage holding ratio of98.7% is achieved with an irradiation energy of 9 J. The ion density isin the range from 10 to 30 pC/cm². The ion density is in the range from30 to 70 pC/cm² in the result represented by the line connecting symbols∘.

Any of FIGS. 30 to 32 show a result of an examination on a relationshipbetween the purity of the monofunctional monomers and voltage holdingratio at an injection hole of a liquid crystal cell. The monofunctionalmonomers used in the present mode for carrying out the invention wasacrylate liquids, and the height value of their purity was 99.4%. It wasrevealed that a monomer allows a higher voltage holding ratio to beachieved the higher the purity of the monomer and that monomers havingpurity of 98.5% or more are suitable for the purpose of eliminatingirregularities at an injection hole. A mixed liquid crystal (alignmentassisting material) preferably included 0% polymerization initiator inorder to achieve a high voltage holding ratio and a low ion density.

A high voltage holding ratio was obtained when there was no unreactedresidue of a bifunctional monomer and a polymerization initiator in apanel after vertical alignment was achieved even though there was someunreacted residue of a monofunctional monomer in the mixed liquidcrystal. At this time, it was required that the reaction proceed untilthe ratio of the unreacted part of the monofunctional monomer (theamount of the residue of the monofunctional monomer in the liquidcrystal layer in the panel divided by the amount of the monofunctionalmonomer added in the mixed liquid crystal) increases from 5% to 50%.

FIG. 30 shows a result of an examination on a relationship betweenirradiation energy and voltage holding ratio performed with the purityof the monofunctional monomer D shown in FIG. 23 varied. The lineconnecting symbols ∘ in the figure represents a monofunctional monomer Dhaving purity of 99.4%. The line connecting symbols ▴ in the figurerepresents a monofunctional monomer D having purity of 98.8%. The lineconnecting symbols ▪ in the figure represents a monofunctional monomer Dhaving purity of 97.7%. The line connecting symbols ⋄ in the figurerepresents a monofunctional monomer D having purity of 94.4%. The lineconnecting symbols x in the figure represents a monofunctional monomer Dhaving purity of 91.7%. In any case, the bifunctional monomer B is addedin an amount that is twice the amount proposed in the related art, andthe polymerization initiator G is also added. The examples shown in FIG.30 were in an atmosphere at 50° C. for 1.67 seconds, and the irradiationenergy density was 0.5 mW/cm². The monofunctional monomers D havingimpurity of 94.4% or more resulted in voltage holding ratio in the rangefrom 86 to 88% and ion densities in the range from 228 to 224 pC/cm².The monofunctional monomer D having impurity of 91.7% resulted in avoltage holding ratio of 37% and an ion density of 1370 pC/cm². It isapparent from FIG. 30 that a monofunctional monomer D provides a highervoltage holding ratio, the higher the purity of the monomer.

FIG. 31 shows a result of an examination on a relationship betweenirradiation energy and voltage holding ratio depending on differences inpurity between the monofunctional monomers D, the examination havingbeen conducted under the same conditions except that the amount of thebifunctional monomers was increased by a factor of 2.4. In the figure,the lines connecting symbols ∘, ▴, ▪, ⋄ and x, respectively, indicatemonofunctional monomers D which were the same in purity as therespective ones in FIG. 30. In any of the samples, the bifunctionalmonomer B was added in an amount that was 2.4 times that in FIG. 30, andthe polymerization initiator G was also added. At an irradiation energyof 6 J/cm², the monofunctional monomers D having impurity of 94.4% ormore resulted in voltage holding ratio in the range from 95 to 97% andion densities in the range from 61 to 84 pC/cm². The monofunctionalmonomer D having purity of 91.7% resulted in a voltage holding ratio of84% and an improved ion density of 416 pC/cm². FIG. 31 also indicatesthat a monofunctional monomer D results in a higher voltage holdingratio, the higher the purity of the monomer. FIG. 31 also indicates thatit is preferable to increase the amount of the bifunctional monomer Band to use a monofunctional monomer D having high purity especially inthe region of an injection hole.

FIG. 32 is a graph in which the purity (GC %) of monofunctional monomersD are plotted along the abscissa axis and voltage holding ratio (%) areplotted along the ordinate axis. The purity substantially linearlychanged from 94.4% up to 99.4%, and changes in the voltage holding ratiowere in the range from 97.2% to 97.5%.

FIG. 33 shows a section of a liquid crystal panel which is suitable foruse in the present mode for carrying out the invention. In the liquidcrystal panel shown in FIG. 33, color filter layers 32 are formed on onesubstrate 21 in addition to active elements 33 such as TFTs and pixelelectrodes 34. Such elements and electrodes are not formed on anothersubstrate 22 in a face-to-face relationship, and only an oppositeelectrode 35 is formed on the same. No light shield layer is formed atleast in a display area. When the substrates 21 and 22 are combined witha predetermined cell gap left therebetween to seal a liquid crystal 5which is mixed with a monomer, since there is no light-blocking membersuch as bus lines and BM (black matrix) layer, the liquid crystal 5mixed with a monomer can be efficiently irradiated with UV light fromthe side of the substrate 22.

FIG. 34 shows a section of a liquid crystal panel which is also suitablefor use in the present mode for carrying out the invention. In theliquid crystal panel shown in FIG. 34, color filters 32 are formed onone substrate 21 in addition to active elements 33 such as TFTs andpixel electrodes 34. Another substrate 22 facing the above substrate isformed of a plastic material or film material, and only an oppositeelectrode 35 is formed on the substrate 22.

When the substrates 21 and 22 are combined with a predetermined cell gapleft therebetween to seal a liquid crystal 5 which is mixed with amonomer, since there is no light-blocking member such as bus lines, theliquid crystal 5 mixed with a monomer can be efficiently irradiated withUV light from the side of the substrate 22. At this time, in case thatthe mixed crystal 5 includes a polymerization initiator, it isadvantageous to use a polymerization initiator which has highlight-absorbing properties in the region of visible light. Sinceirradiation with ultraviolet rays is not preferable to preventdeterioration of the plastic or film substrate, the mixed crystal 5 isirradiated with visible light from the side of the substrate 22, and themixed crystal 5 is thus efficiently irradiated with light.

The liquid crystal panel in the present mode for carrying out theinvention is suitable for fabrication using the so-called dispenserinjection method in which a mixed liquid crystal is dispensed to atleast one substrate and another substrate is thereafter combined withthe same. Steps for manufacturing a liquid crystal display panelaccording to the dispenser injection method will be briefly describedwith reference to FIGS. 35A to 35C. First, as shown in 35A, a liquidcrystal 206 is dispensed from a liquid crystal dispenser which is notshown to a plurality of positions on a surface of an array substrate 21having switching elements such as TFTs and color filters formed thereon.Next, an opposite substrate 22 is aligned with and bonded to the arraysubstrate 21, the opposite substrate having a common electrode formed ina display area thereof and having a UV seal material 202 applied aroundthe display area which is cured when irradiated with ultraviolet rays(UV). This step is performed in vacuum. When the combined substrates arethen returned into the atmosphere, the liquid crystal 206 between thecombined array substrate 21 and the opposite substrate 22 is dispersedby the atmospheric pressure as shown in FIG. 35B. Then, the sealmaterial 202 is irradiated with UV light by a UV light source 208 thatis moved in a moving direction 211 along the region where the sealmaterial 202 is applied as shown in FIG. 35C, whereby the seal material202 is cured.

The use of the dispenser injection method in panel manufacturing stepsis strongly desired because it provides the possibility of a reductionin the panel manufacturing cost and an improvement in mass productivityfor a first reason that it allows a significant reduction in the amountof the liquid crystal material used and a second reason that it allows areduction in the liquid crystal injection time in comparison to thevacuum injection method which has been widely used for panel manufacturein the related art. The method is also advantageous in that iteliminates the need for liquid crystal injection holes 14 that areopenings in a seal material 12 as shown in FIG. 19.

The use of the dispenser injection method makes it possible to fabricatea liquid crystal panel by dispensing two or more kinds of mixed liquidcrystals instead of one kind of mixed crystal. For example, as shown inFIG. 36A, a mixed liquid crystal dispensed may comprise a liquid crystalLca which is a liquid crystal material including no alignment assistingmaterial, a liquid crystal Lcb which is a mixture of a liquid crystalmaterial and a monofunctional monomer, a liquid crystal Lcc which is amixture of a liquid crystal material and a bifunctional monomer, aliquid crystal Lcd which is a mixture of a liquid crystal material, amonofunctional monomer, and a bifunctional monomer and a liquid crystalLce which is a mixture of a liquid crystal material and a polymerizationinitiator. A liquid crystal panel having high reliability can befabricated by at least two kinds or more among them.

As shown in FIG. 36B, a liquid crystal material Lc may be dispensed ontoa substrate 21 by a dispenser (not shown) containing only the liquidcrystal material Lc (first dispensing), and a monomer material α maythen be dispensed onto the liquid crystal material Lc on the substrate21 by a dispenser (not shown) containing only the monomer material α(second dispensing) to mix them.

Alternatively, as shown in FIG. 36C, the liquid crystal material Lcalone or a liquid that is a mixture of the liquid crystal material Lcand the monomer material α may be dispensed; different monomer materialsβ and γ may be dispensed on an opposite substrate; and the substrates 21and 22 may be combined to produce various kinds of mixed crystals.

A detailed description will now be made with reference to embodimentsand comparative examples.

Embodiment 4-1

Each of a pair of glass substrate having transparent electrodes (ITOfilms) patterned thereon was washed. Spacers of 4.0 μm were dispersed onone glass substrate, and a thermoset seal was applied to another glasssubstrate by a dispenser. Those substrates were combined to fabricate anopen cell. A liquid crystal A (Δ∈=−3.8) and a resin were mixed in aratio of 98:2 by weight. The resin was obtained by mixing amonofunctional monomer D and a bifunctional monomer B in a ratio of 15:1by weight. A polymerization initiator G was mixed at 2.5% by weight ofthe total weight of the monofunctional monomer and the bifunctionalmonomer.

The mixed liquid crystal thus prepared was charged into the open cellusing the vacuum injection method, and the injection hole was sealedwith a visible light-cured resin. The liquid crystal cell was irradiatedwith ultraviolet rays (UV) having intensity of 0.5 mW/cm². Therelationship between survivability against irradiation energy andvoltage holding ratio was as shown FIG. 22. The liquid crystal cell wasprocessed at each required irradiation energy, and voltage holding ratiowere measured. The liquid crystal cell was disassembled, and thesurvival rate of each material was obtained from the collected liquidcrystal using a gas chromatographic analysis. While the survival rate ofeach material became smaller the greater the irradiation energy, about10% of the monofunctional monomer survived even when irradiated with anenergy of 15 J/cm². In the range in which the survival rate greatlydecreased, the voltage holding ratio increased greatly. However, theincrease in the holding ratio became small when the change in thesurvival rate became small.

The voltage holding ratio were measured using an apparatus VHR-1manufactured by TOYO Corporation, and the measurement was conducted at ameasuring temperature of 50° C. and a holding time of 1.67 s.

Embodiment 4-2

FIG. 23 shows a result of an examination of the specific resistance ofmixed crystals obtained by adding components of an alignment assistingmaterial in a liquid crystal A. The liquid crystal A is the same as thatused in Embodiment 4-1. When nothing was added, the liquid crystal had aspecific resistance on the level of 10¹⁴ before being heated. Whenheated, the specific resistance decreased to the level of 10¹³. Thereduction was on the same level as that of an ordinary mixed liquidcrystal mixed with no alignment assisting material. The specificresistance of mixed liquid crystals AB and AC added with thebifunctional monomers B and C, respectively, decreased to the level of10¹³, whereas the resistance of mixed liquid crystals AD and AE addedwith the monofunctional monomers D and E respectively decreased to thelevel of 10¹¹.

Embodiment 4-3

An open cell similar to those in Embodiment 4-1 was fabricated. A mixedliquid crystal having a mixing ratio different from that of the mixedliquid crystal in Embodiment 4-1 was prepared. The mixed liquid crystalwas obtained by mixing a liquid crystal A (Δ∈=−3.8) with a resin in aratio of 98:2 by weight. The resin was a mixture of a monofunctionalmonomer D and a bifunctional monomer B in a ratio of 15:2.4 by weight. Apolymerization initiator G was mixed at 2.5% by weight of the totalweight of the monofunctional monomer and the bifunctional monomer. Themixed liquid crystal thus prepared was charged and sealed in a waysimilar to that in Embodiment 4-1. The liquid crystal cell wasirradiated with ultraviolet rays (UV) at an intensity of 0.5 mW/cm².FIGS. 24 to 29 show results of a comparison between the relationships ofvoltage holding ratio to irradiation energy with the results of theEmbodiment 4-1. The voltage holding ratio could be improved at both of acentral part and an injection hole of the liquid crystal cell. While thevoltage holding ratio of the mixed liquid crystal in Embodiment 4-1 wason the level of 70%, the mixed liquid crystal of the present embodimenthad an improved voltage holding ratio on the level of 97%. There was adifference between their ion densities, i.e., the density range of 300to 500 pC/cm² could be reduced to 50 to 90 pC/cm².

Embodiment 4-4

An open cell similar to that in Embodiment 4-1 was fabricated. A mixedliquid crystal different from that in Embodiment 4-3 was prepared. Themixed liquid crystal of the present embodiment had a composition similarto the mixed liquid crystal in Embodiment 4-3 except that thepolymerization initiator G was excluded. FIGS. 28 and 29 show results ofan examination similar to that in Embodiment 4-3 carried out on themixed liquid crystal excluding the polymerization initiator G thusprepared. The voltage holding ratio could be further improved from thatin Embodiment 4-3 at both of the central part and injection hole of theliquid crystal cell. The voltage holding ratio could be improved to thelevel of 98% at both of the central part and injection hole. The iondensity could be halved from that in Embodiment 4-3.

Embodiment 4-5

A mixed liquid crystal based on Embodiment 4-1 and a mixed liquidcrystal based on Embodiment 4-3 were prepared. Both of the liquidcrystals were obtained by mixing the liquid crystal A (Δ∈=−3.8) with aresin in a ratio of 98:2 by weight. The weight ratios of themonofunctional monomer D and the bifunctional monomer B were the same asthose in Embodiments 4-1 and 4-3, and the polymerization initiator G wasalso mixed in 2.5% by weight of the total weight. An examination wascarried out by varying the purity of the monofunctional monomer D.Specifically, a monofunctional monomer D1 having purity of 91.7%, amonofunctional monomer D2 having purity of 94.4%, a monofunctionalmonomer D3 having purity of 97.7%, a monofunctional monomer D4 havingpurity of 98.8% and a monofunctional monomer D5 having purity of 99.4%were used. A comparison of voltage holding ratio similar to that inEmbodiment 4-3 revealed that a higher voltage holding ratio can beachieved, the higher the purity of a monomer, as shown in FIGS. 30, 31and 32.

Fifth Mode for Carrying Out the Invention

A liquid crystal display and a method of manufacturing the same in afifth mode for carrying out the invention will now be described. Amongactive matrix type liquid crystal displays, reflective liquid crystaldisplays which can be light-weight, thin and less power-consuming arerecently attracting attention and are disclosed in the above-mentionedPatent Document 2 and Patent Document 3, for example. Any of suchdisplays employs a method utilizing a TN liquid crystal in which theliquid crystal is twisted and aligned by performing a rubbing process onan alignment film. However, in the method disclosed in the PatentDocument 2 for example, a problem arises in that alignment controlthrough rubbing is difficult to perform because irregularities areformed on reflective pixel electrodes.

It is an object of the present mode for carrying out the invention tosolve the above-described problem, to simplify processing, to reduce themanufacturing cost, and to improve the yield of manufacture. A techniqueis used to control the alignment of a liquid crystal without using arubbing process. Methods have been disclosed in Patent Document 4 andothers in which processing is simplified by injecting a positive liquidcrystal (a liquid crystal having a positive dielectric constantanisotropy) between horizontal alignment films which have not beensubjected to an aligning process. However, such methods necessitate astep of injecting a liquid crystal material between substrates at atemperature equal to or higher than a temperature at which transition ofthe liquid crystal into an isotropic phase takes place. The methods alsonecessitate some limitations on manufacturing steps, the limitationsbeing different from those in injecting methods in the related art andincluding a need for rapid cooling at a rate of 10° C./sec or more atthe time of phase transition from the isotropic phase to the liquidcrystal phase. Further, since a liquid crystal has a small pre-tiltangle in horizontal alignment, the stability of alignment at irregularelectrodes as disclosed in Patent Document 2 is lower than thatachievable with the rubbing method.

In the present mode for carrying out the invention, solid stateproperties of a vertical alignment film are controlled to provide aliquid crystal display which does not need an aligning process such asrubbing during injection at the room temperature similar to injection inthe related art. The method will not cause any problem in aligningproperties when used in a reflective liquid crystal display ortransflective liquid crystal display having reflective electrodes in anunevenness configuration, to say noting of a transmissive liquid crystaldisplay.

Referring to the technique specifically, in normal processing of aliquid crystal display utilizing the MVA method that is a VA typealignment control method originated with the applicant, it is necessaryto form vertical alignment films mainly composed of polyamic acid orpolyimide on TFT and CF substrates using the printing method or spincoat method and to complete the alignment films through two bakingsteps, i.e., pre-baking and post-baking steps. The present mode forcarrying out the invention is a method in which a monomer, an oligomer,and a polymer having one or more kinds of functional groups are mixed ina liquid crystal layer and are reacted (polymerized or cross-linked)with each other using UV light (electromagnetic wave) to achievevertical alignment instead of forming alignment films on CF and TFTsubstrates. It is also a technique which makes it possible to improvethe reliability, manufacturing cost, and manufacturing tact time ofliquid crystal panels significantly.

The present mode for carrying out the invention may be applied totransmissive, reflective or transflective LCDs. Referring to the modesof liquid crystal layers, the invention is advantageous in any of TN,OCB, VA (MVA), HAN (Hybrid Aligned Nematic) and IPS (In-Plane Switching)modes.

The use of the present mode for carrying out the invention makes itpossible to provide reliable liquid crystal displays at a low cost witha high yield of manufacture.

Embodiment 5-1

A liquid crystal obtained by mixing a UV-cured acrylate monomer and amethacrylate monomer (and a polymerization initiator if the reactionrate is to be improved) in an n-type chiral nematic liquid crystalhaving negative dielectric constant anisotropy added with a chiralmaterial is injected into an open cell formed by MVA type TFT and CF(color filter) substrates having no alignment film formed thereon. Thecell is then irradiated with UV light from the side of the CF substrateto form polymer films that induce vertical alignment at interfacesbetween the substrates and the liquid crystal, thereby achievingvertical alignment.

At this time, the vertically aligning power can be further controlled byproviding the substrate surfaces with surface energy by irradiating thesame with UV light (preferably, UV light having a wavelength of 365 nmor less) or performing a thermal process or chemical process (a processusing an organic solvent such as NMP) on the same. The chiral materialmixed in the liquid crystal also results in a certain tendency, andsufficient aligning properties can be obtained under any of d/pconditions of 0.9, 0.18 and 0.35 (where p represents the chiral pitchand d represents the cell gap).

Embodiment 5-2

There is provided a reflective liquid crystal display in whichreflective electrodes having unevenness are formed on a TFT substrate ora transflective liquid crystal display which has a transmissive regionin part thereof. A liquid crystal obtained by mixing a UV-cured acrylatemonomer and a methacrylate monomer (and a polymerization initiator ifthe reaction rate is to be improved) in an n-type chiral nematic liquidcrystal having negative dielectric constant anisotropy added with achiral material is injected into an open cell formed by TFT and CFsubstrates having no alignment film formed thereon. The cell is thenirradiated with UV light from the side of the CF substrate to formpolymer films that induce vertical alignment at interfaces between thesubstrates and the liquid crystal, thereby achieving vertical alignment.The resultant panel is then sandwiched by circular polarization platesto provide the reflective or transflective liquid crystal display.

Embodiment 5-3

A liquid crystal display employing a color display method using colorfilters in three primary colors R, G and B can be provided by combiningEmbodiment 5-1 or 5-2 with a multi-gap technique in which at least onekind of sub-pixels among sub-pixels in R, G and B are different fromothers in the cell thickness. In this case, retardation Δnd of theliquid crystal layer (Δn represents the birefringence of the liquidcrystal layer and d represents the cell gap) is preferably in the rangefrom 150 nm to 500 nm.

As described above, the invention makes it possible to omit the existingstep of forming a vertical alignment film and to thereby allow a costreduction.

The invention also makes it possible to form a vertical alignment filmeasily even if the mother glass is large.

The invention further makes it possible to reduce white lines and tothereby suppress any reduction in contrast.

What is claimed is:
 1. A liquid crystal display comprising: a liquidcrystal material sandwiched between substrates, wherein the liquidcrystal material includes a monomer material having a structureexpressed by:

(where X represents an acrylate group or methacrylate group; Arepresents a benzene ring or cyclohexane ring; R₁ represents an alkylgroup or alkoxy group having carbon atoms in a quantity in the rangefrom 1 to 20; a represents 0 or 1; m represents an integral number inthe range from 0 to 10; and n represents an integral number in the rangefrom 0 to 2); and an ultraviolet-cured substance comprising a systemincluding the monomer material, formed at an interface of thesubstrates.